This invention relates to electronic data processing, and more particularly concerns a method for reducing the amount of time and temporary storage space required for large data files while they are being modified.
The invention is useful in conjunction with editors, word processors, data-base managers, and similar programs which manipulate and modify large collections of data. Editors will be used to exemplify such programs, and the data will be termed a text document.
Editors come in two types, for the present purpose. One type loads a copy of the document from disk or main storage into a separate work file. The editor actually modifies only the data in the work file. At the end of a session, the operator may keep the changes in the new version by replacing the original file with the work file; or, he may choose to exit without update by discarding the work file. The latter is useful as an "undo" capability. Also, a power failure, a rogue global replace, or some other calamity only destroys the changes, not the original document. 0n the other hand, this type of editor doubles the storage space required for the document, and requires a significant amount of time to construct and store the work file. The second type of editor makes modifications directly to the data file containing the original document. They are smaller and faster, but they live dangerously; a malfunction or operator mistake could destroy the entire data file. Most word processors are of the second type, since they usually run in smaller machines with less storage and slower processors.